Accurate gain implementation in CMOS sensor

ABSTRACT

The claimed subject matter provides systems and/or methods that facilitate combining analog and digital gain for utilization with CMOS sensor imagers. The analog gain can provide coarse gain steps and the digital gain can provide finer gain steps between adjacent coarse analog gain values. Further, since analog gain can suffer from low precision, dispersion, etc., on-chip calibration can be implemented to calibrate the analog and digital gain. For example, a digital amplifier can be calibrated to compensate for differences between actual and nominal analog gains associated with one or more analog amplifiers.

BACKGROUND

Recent technological advances have led to CMOS sensor imagers beingleveraged by cameras, video systems, and the like. CMOS sensor imagerscan include an integrated circuit with an array of pixel sensors, eachof which can comprise a photodetector. The signal from the pixel arrayoftentimes can be amplified by one or more on-chip analog amplifiers.The analog amplifiers can provide gain granularity and range to matchrequirements of sophisticated camera functions such as, for instance,automatic gain control (AGC) and white balance (WB), while alsooptimizing dynamic range and noise performance of the CMOS sensorimagers.

Variations in the fabrication process oftentimes can cause non-uniformoperation of the CMOS sensor imagers. For instance, CMOS sensor imagersin disparate fabrication lots or within large batches can exhibitoperating variation. Moreover, performance of CMOS sensor imagers canvary over a period of time (e.g., due to changes in temperature,humidity, . . . ). According to an illustration, non-uniformity inoperation can result from process tolerances of analog componentsincluded with the CMOS sensor imagers.

By way of example, on-chip analog amplifiers can lead to operationvariations. Since analog amplifiers typically can be implemented using aselectable array of analog capacitors, such amplifiers can suffer fromlimited gain precision, gain step size dispersion, non-monotonicbehavior and chip-to-chip gain dispersion. The foregoing are significantlimitations that can become increasingly onerous as the analog step sizeis reduced. For instance, the step size can be decreased from 3 dB to0.1 dB, and thus, the size of the smallest analog capacitor implementedin the analog stage can be decreased by 32 times. Such a reduction ofthe geometrical dimension of the analog capacitor can compromise itsprecision. For high performance applications such as the next generationof hybrid camcorders, even finer gain step sizes can be employed (e.g.,on the order of 0.1 dB to 0.01 dB). Since monotonic behavior andadequate chip-to-chip uniformity are also desired features, conventionalanalog amplifiers associated with CMOS sensor imagers commonly can beineffective for providing small gain step sizes.

SUMMARY

The following presents a simplified summary in order to provide a basicunderstanding of some aspects described herein. This summary is not anextensive overview of the claimed subject matter. It is intended toneither identify key or critical elements of the claimed subject matternor delineate the scope thereof. Its sole purpose is to present someconcepts in a simplified form as a prelude to the more detaileddescription that is presented later.

The claimed subject matter relates to systems and/or methods thatfacilitate combining analog and digital gain for utilization with CMOSsensor imagers. The analog gain can provide coarse gain steps and thedigital gain can provide finer gain steps between adjacent coarse analoggain values. Further, since analog gain can suffer from low precision,dispersion, etc., on-chip calibration can be implemented to calibratethe analog and digital gain. For example, a digital amplifier can becalibrated to compensate for differences between actual and nominalanalog gains associated with one or more analog amplifiers.

In accordance with various aspects of the claimed subject matter, ananalog amplifier and a digital amplifier can operate in conjunction toprovide optimized dynamic range and noise performance (e.g., associatedwith the analog amplifier) and fine step size with high precision andreproducibility (e.g., associated with the digital amplifier) for a CMOSsensor imager. Moreover, the analog amplifier can introduce gaindiscontinuity, dispersion, lack of precision, etc., which can becompensated for by the digital amplifier. Further, a feedback componentcan control calibration of the digital amplifier based upon comparisonsof actual analog gains with nominal analog gains. For example,calibration can be performed by the feedback component during a chipstartup sequence, after a predetermined amount of operating time, uponoccurrence of a condition, event, and the like, during chip production,etc.

The following description and the annexed drawings set forth in detailcertain illustrative aspects of the claimed subject matter. Theseaspects are indicative, however, of but a few of the various ways inwhich the principles of such matter may be employed and the claimedsubject matter is intended to include all such aspects and theirequivalents. Other advantages and novel features will become apparentfrom the following detailed description when considered in conjunctionwith the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an example system that calibratesgain associated with a CMOS sensor imager.

FIG. 2 illustrates a block diagram of an example system that controlsdigital gain compensation where a plurality of analog amplifiers isemployed with a CMOS sensor imager.

FIG. 3 illustrates a block diagram of an example system that employscalibrated amplifier(s) in connection with a CMOS sensor imager.

FIG. 4 illustrates a block diagram of an example system that retainsand/or employs retained calibration data in connection with a CMOSsensor imager.

FIG. 5 illustrates a block diagram of an example system that employsfeedback data to control resources associated with a CMOS sensor imager.

FIG. 6 illustrates a block diagram of an example system that inferswhether analog gain discontinuities are introduced by analogamplifier(s) and/or calibration values that can compensate for suchanalog gain discontinuities.

FIGS. 7-10 illustrate example graphs depicting performance ofuncalibrated and calibrated CMOS sensor imagers.

FIG. 11 illustrates an example methodology that facilitates compensatingfor analog components of a CMOS sensor imager to mitigate gaindispersion.

FIG. 12 illustrates an example methodology that facilitates generatingcalibration coefficients to correct analog gain variations.

FIG. 13 illustrates an example networking environment, wherein the novelaspects of the claimed subject matter can be employed.

FIG. 14 illustrates an example operating environment that can beemployed in accordance with the claimed subject matter.

DETAILED DESCRIPTION

The claimed subject matter is described with reference to the drawings,wherein like reference numerals are used to refer to like elementsthroughout. In the following description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the subject innovation. It may be evident, however,that the claimed subject matter may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form in order to facilitate describing the subjectinnovation.

As utilized herein, terms “component,” “system,” and the like areintended to refer to a computer-related entity, either hardware,software (e.g., in execution), and/or firmware. For example, a componentcan be a process running on a processor, a processor, an object, anexecutable, a program, and/or a computer. By way of illustration, bothan application running on a server and the server can be a component.One or more components can reside within a process and a component canbe localized on one computer and/or distributed between two or morecomputers.

Furthermore, the claimed subject matter may be implemented as a method,apparatus, or article of manufacture using standard programming and/orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer program accessible from anycomputer-readable device, carrier, or media. For example, computerreadable media can include but are not limited to magnetic storagedevices (e.g., hard disk, floppy disk, magnetic strips, . . . ), opticaldisks (e.g., compact disk (CD), digital versatile disk (DVD), . . . ),smart cards, and flash memory devices (e.g., card, stick, key drive, . .. ). Additionally it should be appreciated that a carrier wave can beemployed to carry computer-readable electronic data such as those usedin transmitting and receiving electronic mail or in accessing a networksuch as the Internet or a local area network (LAN). Of course, thoseskilled in the art will recognize many modifications may be made to thisconfiguration without departing from the scope or spirit of the claimedsubject matter. Moreover, the word “exemplary” is used herein to meanserving as an example, instance, or illustration. Any aspect or designdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects or designs.

With reference to FIG. 1, illustrated is a system 100 that calibratesgain associated with a CMOS sensor imager. The system 100 combinesanalog and digital gain; accordingly, advantages typically associatedwith analog amplifiers such as optimized dynamic range and noiseperformance can be yielded by the system 100 along with commonadvantages of digital amplifiers such as fine step size with highprecision and reproducibility. Moreover, the system 100 can acceptdispersion generated by analog components, and compensate for suchdispersion by implementing a correction algorithm that controls digitalcomponents of the system 100. After the correction algorithm, sensorgains can be aligned with greater precision as compared to conventionalsensors that typically employ solely analog components. The system 100can be associated with a CMOS sensor imager utilized in connection witha camcorder, digital camera, microscope, video system, and the like.

The system 100 can include a test signal generator 110 that yields oneor more reference voltages employed for calibration. It is to beappreciated that the test signal generator 110 can be included on a chipwith the CMOS sensor imager (and the corresponding amplifiers).According to another example, the test signal generator 110 can be astand alone device or included within a separate device that providesreference voltage(s); thus, the CMOS sensor imager can receive suchinput reference voltage(s), which can be employed in connection withcalibration of the gain. By way of illustration, the test signalgenerator 110 can output an analog reference voltage. Additionally oralternatively, it is contemplated that a digital signal corresponding tothe reference voltage can be yielded by the test signal generator 110;hence, a digital-to-analog converter (DAC) (not shown) can be employedto convert the digital signal to an analog signal. While the test signalgenerator 110 provides the reference voltages (e.g., duringcalibration), disparate components of the CMOS sensor imager can bedisabled; for example, the reference voltages yielded by the test signalgenerator 110 can substitute for signals commonly obtained by a pixelarray (not shown) of the CMOS sensor imager while the system 100 isoperating in a calibration mode.

An analog amplifier 120 can obtain the reference voltage(s) (e.g., testsignal(s)) and amplify (and/or attenuate) such input voltage(s) to yieldcorresponding output voltage(s). Although one analog amplifier 120 isdepicted, it is to be appreciated that substantially any number ofanalog amplifiers can be employed in combination. The analog amplifier120 can provide a fixed and/or adjustable amount of gain. According toan illustration, the amount of gain yielded by the analog amplifier 120can be selectable (e.g., based upon an input, an operation, a monitoredcondition, a program, . . . ). The analog amplifier 120 can generatecoarse gain steps, for instance, on the order of 1 dB to 3 dB. Further,the analog amplifier 120 can have substantially any gain range (e.g., 0dB to 24 dB, . . . ). Moreover, the analog amplifier 120 can introduce alack of precision and/or dispersion while amplifying the inputvoltage(s). For example, the analog amplifier 120 can generate an outputvoltage from a corresponding input voltage as follows:V_(out)=Gain×(V_(in)+Offset). It is to be appreciated that the analogamplifier 120 can have gain mismatch and/or offset mismatch, andtherefore, the gain and/or the offset can vary between chips, sensors,lots, and the like. The output voltage from the analog amplifier 120 canthereafter be quantized by an analog-to-digital converter (ADC) 130.Accordingly, the ADC 130 can produce a digital output corresponding tothe amplified voltage provided by the analog amplifier 120.

The system 100 can also include a digital amplifier 140 that can obtainthe digital output from the ADC 130 and adjust the gain to compensatefor mismatch (e.g., gain mismatch, offset mismatch, . . . ) introducedby the analog amplifier 120; for example, the digital amplifier 140 canboth be calibrated to compensate for mismatch associated with the analogamplifier 120 (e.g., mitigate the difference between actual and nominalanalog gain) as well as provide fine digital gain steps between adjacentanalog gain steps. The digital amplifier 140 can provide fine gaingranularity, precision, reproducibility and range. For instance, thedigital amplifier 140 can provide an adjustable, digital gain. Moreover,the digital gain can be utilized to provide a fine gain step (e.g., upto 0.001 dB) in between two adjacent coarse analog gain values.Accordingly, the use of the digital amplifier 140 can be restricted to alimited range (e.g., with a maximum range substantially similar to again step size provided by the analog amplifier 120 such as on the orderof 1 dB to 3 dB); thus, sensor performance and resultant image qualitymay not be compromised by utilizing digital amplification in comparisonto conventional digital amplifiers that can yield degraded noiseperformance and sensor dynamic range.

A feedback component 150 controls operation of the digital amplifier140. The feedback component 150 can enable on-chip calibration of thegain generated by the analog amplifier 120 and/or the digital amplifier140. For example, the on-chip calibration effectuated by the feedbackcomponent 150 can be performed as part of a chip power up sequence.Additionally or alternatively, the feedback component 150 can initiatecalibration after a fixed amount of sensor operating time to removepotential drift due to temperature, bias transient, and so forth.According to another illustration, calibration can be effectuated duringproduction; thus, offline calibration by the feedback component 150 canbe performed.

The feedback component 150 can control calibration of the digitalamplifier 140 based upon data obtained from the test signal generator110 (e.g. reference voltage(s)), the analog amplifier 120 (e.g., nominalgain), the ADC 130 (not shown), and/or the digital amplifier 140. By wayof illustration, the feedback component 150 can receive informationcorresponding to a reference voltage provided by the test signalgenerator 110. Additionally, the feedback component 150 can obtaininformation corresponding to the output voltage generated by the analogamplifier 120 (and/or the corresponding digitized output provided by theADC 130). Further, the feedback component 150 can receive controlinformation from the analog amplifier 120 pertaining to a nominal gainstep. Moreover, the feedback component 140 can obtain the digitizedoutput from the digital amplifier 140; the digitized output can enabledetermining the actual gain yielded by the system 100, which can becompared to the nominal gain.

The feedback component 150 can calibrate the digital amplifier 140 basedupon any number of reference voltages provided by the test signalgenerator 110 for a particular analog gain setting (e.g., nominal gain).For instance, a plurality of reference voltages and correspondingdigitized outputs from the digital amplifier 140 can be evaluated by thefeedback component 150 to allow for differential gain calibration sincethe analog amplifier 120 can have gain mismatch as well as offsetmismatch in comparison to disparate analog amplifiers. The offsetmismatch results in the analog amplifier 120 having a slightly differentoutput voltage based upon a reference voltage of zero. The feedbackcomponent 150 can correct excessive analog gain or lack of analog gainby adjusting the digital gain yielded by the digital amplifier 140. Forexample, the feedback component 150 can employ linear regression todetermine an actual gain yielded the analog amplifier 120 for eachnominal gain step of the analog amplifier 120. Moreover, the feedbackcomponent 150 can calculate corrective coefficients for digital gainadjustments provided by the digital amplifier 140 utilized to calibratethe analog amplifier 120 based upon differences between actual gains andcorresponding nominal gains; such corrective coefficients can beemployed by the digital amplifier 140 during operation of the CMOSsensor imager.

Although not shown, it is contemplated that the feedback component 150can control operation of the test signal generator 110 and/or the analogamplifier 120 during calibration. For example, the feedback component150 can select the reference voltage to be output by the test signalgenerator 110. By way of another illustration, the feedback component120 can choose the nominal gain to be employed by the analog amplifier120; however, it is to be appreciated that the claimed subject matter isnot so limited.

Turning to FIG. 2, illustrated is a system 200 that controls digitalgain compensation where a plurality of analog amplifiers is employedwith a CMOS sensor imager. The system 200 can include the test signalgenerator 110 that yields reference voltage(s), which can be provided tothe plurality of analog amplifiers. In particular, the system 200 caninclude two analog amplifiers, namely, a column buffer 210 and aprogrammable gain amplifier 220. The amplified output from theprogrammable gain amplifier 220 can thereafter be digitized by the ADC130. Moreover, the digital amplifier 140 can adjust for excess or lackof analog gain and the feedback component 150 can calibrate gain withinthe system 200 (e.g., by controlling operation of the digital amplifier140).

The CMOS sensor imager can include an array of pixels with M rows and Ncolumns, where M and N can be substantially any integers. Moreover,signals from the pixels can be processed on a column by column basis.Each column of pixels can be associated with a respective column buffer(e.g., the column buffer 210); accordingly, the CMOS sensor imager caninclude N column buffers. The column buffer 210 can enable low noisereadout and can condition the signal from a pixel positioned at one ofthe rows in the column corresponding to the column buffer 210.

The output from each column buffer (e.g., the column buffer 210) canthereafter be amplified by the programmable gain amplifier 220. Theprogrammable gain amplifier 220 can amplify the output from each of thecolumn buffers one at a time. Moreover, a common programmable gainamplifier (e.g., the programmable gain amplifier 220) can be utilized inconnection with amplifying the output of each of the column buffers;however, it is contemplated that more than one programmable gainamplifier can be employed in connection with the system 200. Moreover,the resultant output from the programmable gain amplifier 220 can havean output voltage,V_(out)=G_(PGA)(G_(CB)V_(in)+Offset_(CB))+Offset_(PGA), where G_(PGA) isthe gain from the programmable gain amplifier 220, G_(CB) is the gainfrom the column buffer 210, V_(in) is the input voltage (e.g., referencevoltage) yielded by the test signal generator 110, Offset_(CB) is theoffset introduced by the column buffer 210, and Offset_(PGA) is theoffset introduced by the programmable gain amplifier 220.

The output analog signal from the programmable gain amplifier 220 can bedigitized with the ADC 130 and thereafter input to the digital amplifier140. The digital amplifier 140 can adjust the gain with fine step sizealterations to the digitized input. Such alterations can have highprecision and reproducibility. Moreover, the feedback component 150 canmodify operation of the digital amplifier 140 (e.g. during calibration)based upon the output of the digital amplifier 140, the referencevoltage yielded by the test signal generator 110, the nominal gainutilized by the programmable gain amplifier 220, a combination thereof,and the like. For example, the feedback component 150 can generatecorrective coefficients for each analog amplifier (e.g., any number ofcolumn buffers such as the column buffer 210, the programmable gainamplifier 220, . . . ) during a calibration mode, and the correctivecoefficients can be used during operation of the CMOS sensor imager.

Referring now to FIG. 3, illustrated is a system 300 that employscalibrated amplifier(s) in connection with a CMOS sensor imager. Thesystem 300 includes a pixel array 310 that can include M rows and Ncolumns, where M and N can be any integers. Each pixel in the pixelarray 310 can comprise a photodetector (e.g., a photodiode). Signalsobtained by the pixel array 310 can be processed on a column by columnbasis; thus, a particular row of pixels from the pixel array 310 can beselected to be read. System 300 can include N column buffers 320, whereeach of the column buffers 320 operates in conjunction with a respectivecolumn from the pixel array 310. Although eleven column buffers 320 aredepicted, it is to be appreciated that substantially any number ofcolumn buffers similar to the column buffers 320 can be employed inconnection with the system 300. The content from the pixels in each ofthe columns of the selected row can be transferred to the correspondingcolumn buffers 320, and the column buffers 320 can amplify (e.g.,condition) the signals from the pixels.

After processing by the column buffers 320, outputted values from eachof the column buffers 320 can be retained. Moreover, each of the columnbuffers 320 can be associated with a respective capacitor 330 and switch340. The capacitors 330 can be loaded with the outputted values from thecorresponding column buffers 320. Further, the switches 340 can beclosed one at a time to allow for connecting to a bus 350; thus, thevoltages generated by the column buffers 320 can be multiplexed over thebus 350. The bus 350 can enable communicating each of the outputtedvalues from the respective column buffers 320 to the programmable gainamplifier 220, which can thereafter amplify the signal. The output fromthe programmable gain amplifier 220 can then be digitized by the ADC130. Additionally, the digital amplifier 140 can digitally amplify thedigitized signal as calibrated to yield an output. The digital amplifier140 can adjust the output from the column buffers 320 and theprogrammable gain amplifier 220 to remove gain discontinuitiesintroduced by the respective analog components utilized in connectionwith particular digitized signals; for example, the digital amplifier140 can correct dispersion values associated with the analog gains byamplifying (positive) and/or attenuating (negative) gain values (e.g.,−3 dB to +3 dB digital gain range). Moreover, the digital amplifier 140can amplify (or attenuate) the digitized signal obtained from the ADC130 with fine digital gain steps (e.g., to provide gain with greaterprecision in between analog gain steps).

Turning to FIG. 4, illustrated is a system 400 that retains and/oremploys retained calibration data in connection with a CMOS sensorimager. The system 400 can include the test signal generator 110, theanalog amplifier 120, the ADC 130, the digital amplifier 140, and/or thefeedback component 150 as described above. Further, the system 400 caninclude a data store 410 that can store calibrated gain values to beemployed by the digital amplifier 140. For example, during calibration,the feedback component 150 can retain the calibrated gain values in thedata store 410. Moreover, during operation, the calibrated gain valuescan be retrieved by the digital amplifier 140 from the data store 410;for instance, the digital gain can be coupled to the analog gain in alookup table retained in the data store 410 such that gaindiscontinuities can be removed. Pursuant to an example, calibration canbe effectuated by the feedback component 150 during production to yieldcalibration coefficients; these calibration coefficients can be storedin the data store 410 in a lookup table for utilization (e.g., by thedigital amplifier 140, . . . ) during operation. According to anotherillustration, the feedback component 150 can perform calibration duringa power up sequence to yield a set of calibration values that can belocally and temporarily retained in the data store 410. Moreover,temporarily stored calibration values can be updated during operation toenable readjustment (e.g., after a predetermined number of cycles, uponidentifying a condition, . . . ).

According to an example, a dedicated calibration coefficient can becalculated for each column buffer in the sensor by the feedbackcomponent 150. For instance, for a sensor that includes 1000 columnbuffers, 1000 calibration coefficients can be computed per each gainsetting. Pursuant to another illustration, the computational load can belessened. Following this illustration, rather than calibrating the gainof each column buffer independently, an average gain of the overallcolumn buffer population for each given gain setting can be calibrated;hence, a single calibration coefficient can be generated by the feedbackcomponent 150 per each gain setting regardless of the actual number ofcolumn buffers included on a chip.

The data store 410 can be, for example, either volatile memory ornonvolatile memory, or can include both volatile and nonvolatile memory.By way of illustration, and not limitation, nonvolatile memory caninclude read only memory (ROM), programmable ROM (PROM), electricallyprogrammable ROM (EPROM), electrically erasable programmable ROM(EEPROM), or flash memory. Volatile memory can include random accessmemory (RAM), which acts as external cache memory. By way ofillustration and not limitation, RAM is available in many forms such asstatic RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), doubledata rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM(SLDRAM), Rambus direct RAM (RDRAM), direct Rambus dynamic RAM (DRDRAM),and Rambus dynamic RAM (RDRAM). The data store 410 of the subjectsystems and methods is intended to comprise, without being limited to,these and any other suitable types of memory. In addition, it is to beappreciated that the data store 410 can be a server, a database, a harddrive, and the like.

Now referring to FIG. 5, illustrated is a system 500 that employsfeedback data to control resources associated with a CMOS sensor imager.The system 500 can include the test signal generator 110, the analogamplifier 120, the ACD 130, the digital amplifier 140, and/or thefeedback component 150 as described above. Moreover, the system 500 caninclude an optimization component 510 that can be coupled to thefeedback component 150. The optimization component 510 can utilizeinformation determined from the feedback component 150 to modifyoperation of the CMOS sensor imager. When the feedback component 150determines that the operation of the analog amplifier 120 has changed(e.g., impacting analog gain), the optimization component 510 caneffectuate modifying disparate resources of the CMOS sensor imager tocompensate for such changes. For example, the feedback component 150 candetermine that analog gain dispersion has resulted from an increase intemperature; accordingly, the optimization component 510 can enablealtering fan speed to attempt to reduce the temperature and therebydecrease the analog gain dispersion.

Substantially any device, component, process, operating parameter, etc.associated with the CMOS sensor imager can be adjusted by theoptimization component 510. For instance, the optimization component 510can effectuate changes that impact voltage, temperature, humidity,battery life, environmental conditions, etc. Moreover, alterations toCMOS sensor imager related resources brought forth by the optimizationcomponent 510 can be carried out in conjunction with (and/or instead of)variations to calibration data employed by the digital amplifier 140 asdetermined by the feedback component 150.

Turning to FIG. 6, illustrated is a system 600 that infers whetheranalog gain discontinuities are introduced by analog amplifier(s) and/orcalibration values that can compensate for such analog gaindiscontinuities. The system 600 can include the feedback component 150(and/or the test signal generator 110, the analog amplifier 120, the ADC130, and/or the digital amplifier 140), which can be substantiallysimilar to the aforementioned description. The feedback component 150can further include an intelligent component 610 that can be utilized bythe feedback component 150 to reason about whether analog componentsprovide gain dispersion based upon inputted reference voltages, nominalgains to be employed by analog amplifiers, and/or actual gains yielded.Pursuant to another example, the intelligent component 610 can infervalues of calibration data that can be employed by a digital amplifierto mitigate effects of dispersion caused by analog components.

It is to be understood that the intelligent component 610 can providefor reasoning about or infer states of the system, environment, and/oruser from a set of observations as captured via events and/or data.Inference can be employed to identify a specific context or action, orcan generate a probability distribution over states, for example. Theinference can be probabilistic—that is, the computation of a probabilitydistribution over states of interest based on a consideration of dataand events. Inference can also refer to techniques employed forcomposing higher-level events from a set of events and/or data. Suchinference results in the construction of new events or actions from aset of observed events and/or stored event data, whether or not theevents are correlated in close temporal proximity, and whether theevents and data come from one or several event and data sources. Variousclassification (explicitly and/or implicitly trained) schemes and/orsystems (e.g. support vector machines, neural networks, expert systems,Bayesian belief networks, fuzzy logic, data fusion engines . . . ) canbe employed in connection with performing automatic and/or inferredaction in connection with the claimed subject matter.

A classifier is a function that maps an input attribute vector, x=(x1,x2, x3, x4, xn), to a confidence that the input belongs to a class, thatis, f(x)=confidence(class). Such classification can employ aprobabilistic and/or statistical-based analysis (e.g., factoring intothe analysis utilities and costs) to prognose or infer an action that auser desires to be automatically performed. A support vector machine(SVM) is an example of a classifier that can be employed. The SVMoperates by finding a hypersurface in the space of possible inputs,which hypersurface attempts to split the triggering criteria from thenon-triggering events. Intuitively, this makes the classificationcorrect for testing data that is near, but not identical to trainingdata. Other directed and undirected model classification approachesinclude, e.g. naïve Bayes, Bayesian networks, decision trees, neuralnetworks, fuzzy logic models, and probabilistic classification modelsproviding different patterns of independence can be employed.Classification as used herein also is inclusive of statisticalregression that is utilized to develop models of priority.

Turning to FIGS. 7-10, illustrated are example graphs depictingperformance of uncalibrated and calibrated CMOS sensor imagers. It is tobe appreciated that the claimed subject matter is not limited to suchexamples. With reference to FIG. 7, illustrated is an example graph 700showing uncalibrated analog gain steps together with digital gain steps.The graph 700 plots nominal gains versus actual gains. The analog gainsteps as depicted are 3 dB and the analog range is 24 dB, while thedigital gain steps are 0.2 dB and the digital range is 3 dB. The analoggain steps are represented as dots upon the graph 700 and the digitalgain steps are in between adjacent analog gain steps. FIG. 8 illustratesa graph 800 showing actual gain residuals from data of FIG. 7. Moreparticularly, the graph 800 plots nominal gains versus actual gainresiduals for an example case of using an analog amplifier and a digitalamplifier together without analog gain calibration. Gain discontinuitiesare apparent in the graph 800 in between two adjacent analog gain stepswhen a new analog gain value is selected and the previous analog gain isdeselected.

Turning to FIG. 9, illustrated is a post calibration graph 900 withnominal gains versus actual gains. The dots represent the uncalibratedanalog gains and the squares depict the calibrated values of the analoggains, while the digital gain steps are in between adjacent analogsteps. Thus, digital gain can compensate for variation in the analoggain to mitigate gain discontinuities. On-chip calibration of the analoggain allows for precise measuring of the actual value of each nominalanalog gain step on a chip by chip basis. Further, FIG. 10 illustrates apost calibration residual for actual gain versus nominal gain graph1000. As shown in the graph 1000, the residuals can be zeroed aftercarrying out calibration techniques described herein.

FIGS. 11-12 illustrate methodologies in accordance with the claimedsubject matter. For simplicity of explanation, the methodologies aredepicted and described as a series of acts. It is to be understood andappreciated that the subject innovation is not limited by the actsillustrated and/or by the order of acts, for example acts can occur invarious orders and/or concurrently, and with other acts not presentedand described herein. Furthermore, not all illustrated acts may berequired to implement the methodologies in accordance with the claimedsubject matter. In addition, those skilled in the art will understandand appreciate that the methodologies could alternatively be representedas a series of interrelated states via a state diagram or events.

Turning to FIG. 11, illustrated is a methodology 1100 that facilitatescompensating for analog components of a CMOS sensor imager to mitigategain dispersion. At 1102, a test signal can be obtained. For example,the test signal can be one or more reference voltages. According toanother illustration, the test signal can be received during acalibration mode associated with the CMOS sensor imager. At 1104, ananalog amplification can be applied to the test signal. A nominal gaincan be selected for the analog amplification. Moreover, a plurality oftest signals (e.g., at disparate reference voltages) can be subject tothe analog amplification at a particular nominal gain.

At 1106, nominal gain can be compared to actual gain for the analogamplification. For example, the actual gain related to a particularnominal gain can be determined by analyzing an output voltagecorresponding the amplified test signal measured for each test signal.Moreover, linear regression techniques can be employed upon a pluralityof output voltages pertaining to distinct test signals to yield theactual gain. At 1108, a corrective digital amplification amount (e.g.,corrective digital amplification value) corresponding to the nominalgain can be determined. The corrective digital amplification amount canbe retained in memory (e.g., temporarily, permanently, . . . ). Further,the corrective digital amplification amount can be utilized by a digitalamplifier of the CMOS sensor imager to mitigate the difference betweenthe actual gain and the nominal gain when capturing video. It iscontemplated that the corrective digital amplification amount can bedetermined during production of the CMOS sensor imager, at power up ofthe CMOS sensor imager, after a predetermined amount of time ofoperation of the CMOS sensor imager, upon an occurrence of an eventand/or condition, and the like. Moreover, respective corrective digitalamplification amounts can be determined for each analog amplifier.

Now referring to FIG. 12, illustrated is a methodology 1200 thatfacilitates generating calibration coefficients to correct analog gainvariations. At 1202, gain calibration can be started after a power upsequence. It is to be appreciated, however, that gain calibration can beeffectuated after a predetermined amount of time, upon the occurrence ofa condition, etc. Moreover, gain calibration can be performed duringchip production. Upon entering a calibration mode, certain componentscan be switched off (e.g., pixel array need not be employed duringcalibration, . . . ). At 1204, an internal test voltage can be connectedto a column buffer (CB) input. Substantially any number of columnbuffers can be employed in connection with the claimed subject matter,where each of the column buffers can be utilized with a respectivecolumn of a pixel array of the CMOS sensor imager during video capture.At 1206, a programmable gain amplifier (PGA) and a digital gain can beset to zero.

At 1208, CB gain can be selected G_(CB) _(—) N (e.g., nominal gain stepfor the column buffer can be chosen). At 1210, a test signal can be setto level n. The test signal can be obtained from an on-chip source, aseparate device, and the like. Moreover, the test signal can besubstantially any reference voltage (e.g., input voltage). At 1212, thetest signal value VADCn (e.g., amplified output) can be digitized andstored. Thus, the test signal as amplified by the column buffer can beconverted to a digital output and retained in memory. At 1214, it can bedetermined whether to increase the test signal voltage. If the testsignal voltage is to be increased, the methodology 1200 returns to 1210.The test signal voltage can be increased to yield additionalinput/output voltage pairs to decipher an actual analog gain. Thus, acalibration loop per each analog gain step can be provided where aplurality of analog test signals can be coupled to the analog gain stageinput and the corresponding digitized outputs can be recorded. If thetest signal voltage is not to be increased, the methodology 1200continues to 1216, where linear regression of stored values of the testsignal voltage n and the test signal value VADCn can yield a measuredgain GM_N. Accordingly, actual gain can be computed for each nominalgain step by use of, for instance, linear regression performed on therecorded data (e.g., from 1212). At 1218, the values of the nominalcolumn buffer gain G_(CB) _(—) N and the actual, measured gain GM_N canbe stored. For example, the actual and nominal gains can be retained ina gain lookup table.

At 1220, a determination can be made as to whether to analyze a nextcolumn buffer gain (e.g., nominal column buffer gain). If a next columnbuffer gain is to be evaluated, the methodology returns 1200 to 1208;else, the methodology 1200 continues to 1222. At 1222, upon the columnbuffer gains being tested, computation of digital gain adjustments canbegin. The digital gain adjustments can continue at 1224. At 1226, thestored values (e.g., from 1218) can be obtained. At 1228, correctivecoefficients can be calculated. Through utilization of the gain lookuptable, digital gain can be coupled to the analog gain such that gaindiscontinuities can be mitigated. For example, the digital gain can bepositive (amplification) and/or negative (attenuation) to correctdispersion values associated with the analog gain. Although FIG. 12relates to calibrating column buffer gain, it is to be appreciated thatsimilar calibration can be effectuated for any disparate type of analoggain (e.g. associated with the PGA).

According to another example (not shown), a single calibrationcoefficient associated with the population of column buffers at eachgain setting can be generated. Following this example, at 1212, themethod 1200 can enable digitizing each column buffer output, averagingthe plurality of column buffer outputs, and storing the averaged columnbuffer output values VADCn. Thus, averaging can be introduced afterdigitalization to compute a mean output from the set of column buffersand the average value can be stored with the test signal n to mitigatehardware utilization (e.g., reduce memory usage, number of estimationoperations, . . . ). Further, a single linear regression estimation canbe performed (e.g., at 1216) on the computed average output value thatrepresents the average response of the whole column buffer population ofthe sensor, rather than computing a linear regression per each columnbuffer individually.

In order to provide additional context for implementing various aspectsof the claimed subject matter, FIGS. 13-14 and the following discussionis intended to provide a brief, general description of a suitablecomputing environment in which the various aspects of the subjectinnovation may be implemented. For instance, FIGS. 13-14 set forth asuitable computing environment that can be employed in connection withcalibrating and/or utilizing calibrated amplification associated withCMOS sensor imagers. While the claimed subject matter has been describedabove in the general context of computer-executable instructions of acomputer program that runs on a local computer and/or remote computer,those skilled in the art will recognize that the subject innovation alsomay be implemented in combination with other program modules. Generally,program modules include routines, programs, components, data structures,etc., that perform particular tasks and/or implement particular abstractdata types.

Moreover, those skilled in the art will appreciate that the inventivemethods may be practiced with other computer system configurations,including single-processor or multi-processor computer systems,minicomputers, mainframe computers, as well as personal computers,hand-held computing devices, microprocessor-based and/or programmableconsumer electronics, and the like, each of which may operativelycommunicate with one or more associated devices. The illustrated aspectsof the claimed subject matter may also be practiced in distributedcomputing environments where certain tasks are performed by remoteprocessing devices that are linked through a communications network.However, some, if not all, aspects of the subject innovation may bepracticed on stand-alone computers. In a distributed computingenvironment, program modules may be located in local and/or remotememory storage devices.

FIG. 13 is a schematic block diagram of a sample-computing environment1300 with which the claimed subject matter can interact. The system 1300includes one or more client(s) 1310. The client(s) 1310 can be hardwareand/or software (e.g., threads, processes, computing devices). Thesystem 1300 also includes one or more server(s) 1320. The server(s) 1320can be hardware and/or software (e.g., threads, processes, computingdevices). The servers 1320 can house threads to perform transformationsby employing the subject innovation, for example.

One possible communication between a client 1310 and a server 1320 canbe in the form of a data packet adapted to be transmitted between two ormore computer processes. The system 1300 includes a communicationframework 1340 that can be employed to facilitate communications betweenthe client(s) 1310 and the server(s) 1320. The client(s) 1310 areoperably connected to one or more client data store(s) 1350 that can beemployed to store information local to the client(s) 1310. Similarly,the server(s) 1320 are operably connected to one or more server datastore(s) 1330 that can be employed to store information local to theservers 1320.

With reference to FIG. 14, an exemplary environment 1400 forimplementing various aspects of the claimed subject matter includes acomputer 1412. The computer 1412 includes a processing unit 1414, asystem memory 1416, and a system bus 1418. The system bus 1418 couplessystem components including, but not limited to, the system memory 1416to the processing unit 1414. The processing unit 1414 can be any ofvarious available processors. Dual microprocessors and othermultiprocessor architectures also can be employed as the processing unit1414.

The system bus 1418 can be any of several types of bus structure(s)including the memory bus or memory controller, a peripheral bus orexternal bus, and/or a local bus using any variety of available busarchitectures including, but not limited to, Industrial StandardArchitecture (ISA), Micro-Channel Architecture (MSA), Extended ISA(EISA), Intelligent Drive Electronics (IDE), VESA Local Bus (VLB),Peripheral Component Interconnect (PCI), Card Bus, Universal Serial Bus(USB), Advanced Graphics Port (AGP), Personal Computer Memory CardInternational Association bus (PCMCIA), Firewire (IEEE 1394), and SmallComputer Systems Interface (SCSI).

The system memory 1416 includes volatile memory 1420 and nonvolatilememory 1422. The basic input/output system (BIOS), containing the basicroutines to transfer information between elements within the computer1412, such as during start-up, is stored in nonvolatile memory 1422. Byway of illustration, and not limitation, nonvolatile memory 1422 caninclude read only memory (ROM), programmable ROM (PROM), electricallyprogrammable ROM (EPROM), electrically erasable programmable ROM(EEPROM), or flash memory. Volatile memory 1420 includes random accessmemory (RAM), which acts as external cache memory. By way ofillustration and not limitation, RAM is available in many forms such asstatic RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), doubledata rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM(SLDRAM), Rambus direct RAM (RDRAM), direct Rambus dynamic RAM (DRDRAM),and Rambus dynamic RAM (RDRAM).

Computer 1412 also includes removable/non-removable,volatile/non-volatile computer storage media. FIG. 14 illustrates, forexample a disk storage 1424. Disk storage 1424 includes, but is notlimited to, devices like a magnetic disk drive, floppy disk drive, tapedrive, Jaz drive, Zip drive, LS-100 drive, flash memory card, or memorystick. In addition, disk storage 1424 can include storage mediaseparately or in combination with other storage media including, but notlimited to, an optical disk drive such as a compact disk ROM device(CD-ROM), CD recordable drive (CD-R Drive), CD rewritable drive (CD-RWDrive) or a digital versatile disk ROM drive (DVD-ROM). To facilitateconnection of the disk storage devices 1424 to the system bus 1418, aremovable or non-removable interface is typically used such as interface1426.

It is to be appreciated that FIG. 14 describes software that acts as anintermediary between users and the basic computer resources described inthe suitable operating environment 1400. Such software includes anoperating system 1428. Operating system 1428, which can be stored ondisk storage 1424, acts to control and allocate resources of thecomputer system 1412. System applications 1430 take advantage of themanagement of resources by operating system 1428 through program modules1432 and program data 1434 stored either in system memory 1416 or ondisk storage 1424. It is to be appreciated that the claimed subjectmatter can be implemented with various operating systems or combinationsof operating systems.

A user enters commands or information into the computer 1412 throughinput device(s) 1436. Input devices 1436 include, but are not limitedto, a pointing device such as a mouse, trackball, stylus, touch pad,keyboard, microphone, joystick, game pad, satellite dish, scanner, TVtuner card, digital camera, digital video camera, web camera, and thelike. These and other input devices connect to the processing unit 1414through the system bus 1418 via interface port(s) 1438. Interfaceport(s) 1438 include, for example, a serial port, a parallel port, agame port, and a universal serial bus (USB). Output device(s) 1440 usesome of the same type of ports as input device(s) 1436. Thus, forexample, a USB port may be used to provide input to computer 1412, andto output information from computer 1412 to an output device 1440.Output adapter 1442 is provided to illustrate that there are some outputdevices 1440 like monitors, speakers, and printers, among other outputdevices 1440, which require special adapters. The output adapters 1442include, by way of illustration and not limitation, video and soundcards that provide a means of connection between the output device 1440and the system bus 1418. It should be noted that other devices and/orsystems of devices provide both input and output capabilities such asremote computer(s) 1444.

Computer 1412 can operate in a networked environment using logicalconnections to one or more remote computers, such as remote computer(s)1444. The remote computer(s) 1444 can be a personal computer, a server,a router, a network PC, a workstation, a microprocessor based appliance,a peer device or other common network node and the like, and typicallyincludes many or all of the elements described relative to computer1412. For purposes of brevity, only a memory storage device 1446 isillustrated with remote computer(s) 1444. Remote computer(s) 1444 islogically connected to computer 1412 through a network interface 1448and then physically connected via communication connection 1450. Networkinterface 1448 encompasses wire and/or wireless communication networkssuch as local-area networks (LAN) and wide-area networks (WAN). LANtechnologies include Fiber Distributed Data Interface (FDDI), CopperDistributed Data Interface (CDDI), Ethernet, Token Ring and the like.WAN technologies include, but are not limited to, point-to-point links,circuit switching networks like Integrated Services Digital Networks(ISDN) and variations thereon, packet switching networks, and DigitalSubscriber Lines (DSL).

Communication connection(s) 1450 refers to the hardware/softwareemployed to connect the network interface 1448 to the bus 1418. Whilecommunication connection 1450 is shown for illustrative clarity insidecomputer 1412, it can also be external to computer 1412. Thehardware/software necessary for connection to the network interface 1448includes, for exemplary purposes only, internal and externaltechnologies such as, modems including regular telephone grade modems,cable modems and DSL modems, ISDN adapters, and Ethernet cards.

What has been described above includes examples of the subjectinnovation. It is, of course, not possible to describe every conceivablecombination of components or methodologies for purposes of describingthe claimed subject matter, but one of ordinary skill in the art mayrecognize that many further combinations and permutations of the subjectinnovation are possible. Accordingly, the claimed subject matter isintended to embrace all such alterations, modifications, and variationsthat fall within the spirit and scope of the appended claims.

In particular and in regard to the various functions performed by theabove described components, devices, circuits, systems and the like, theterms (including a reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., a functional equivalent), even though not structurallyequivalent to the disclosed structure, which performs the function inthe herein illustrated exemplary aspects of the claimed subject matter.In this regard, it will also be recognized that the innovation includesa system as well as a computer-readable medium havingcomputer-executable instructions for performing the acts and/or eventsof the various methods of the claimed subject matter.

In addition, while a particular feature of the subject innovation mayhave been disclosed with respect to only one of several implementations,such feature may be combined with one or more other features of theother implementations as may be desired and advantageous for any givenor particular application. Furthermore, to the extent that the terms“includes,” and “including” and variants thereof are used in either thedetailed description or the claims, these terms are intended to beinclusive in a manner similar to the term “comprising.”

What is claimed is:
 1. A system that calibrates gain associated with a sensor imager, comprising: a plurality of analog amplifiers configured to, for a plurality of nominal analog gain settings, obtain and amplify a test signal during calibration to yield amplified outputs respectively corresponding to the plurality of analog amplifiers, wherein the plurality of analog amplifiers comprise a plurality of column buffers; a digital amplifier configured to adjust the amplified outputs based upon a calibration to compensate for mismatch introduced by the plurality of analog amplifiers; and a feedback component configured to, for each nominal analog gain setting of the plurality of nominal analog gain settings, compare the nominal analog gain setting with an average of actual analog gains respectively measured for the plurality of column buffers set to the nominal analog gain setting to yield a plurality of calibration values respectively corresponding to the plurality of nominal analog gain settings, and to control the calibration of the digital amplifier based upon at least one of the plurality of calibration values.
 2. The system of claim 1, further comprising an analog-to-digital converter configured to digitize the amplified outputs to yield a digitized amplified output and to provide the digitized amplified output to the digital amplifier.
 3. The system of claim 1, further comprising a test signal generator configured to yield the test signal.
 4. The system of claim 1, wherein the plurality of column buffers each amplify a signal from a respective column of a pixel array.
 5. The system of claim 4, further comprising at least one programmable gain amplifier configured to amplify an output from the plurality of column buffers.
 6. The system of claim 1, wherein the feedback component is further configured to control calibration corresponding to each of the plurality of analog amplifiers.
 7. The system of claim 1, wherein the digital amplifier is further configured to generate finer gain steps than the plurality of analog amplifiers.
 8. The system of claim 1, wherein the feedback component is further configured to perform the calibration as part of a chip power up sequence.
 9. The system of claim 1, wherein the feedback component is further configured to perform the calibration after a predetermined amount of sensor operating time.
 10. The system of claim 1, wherein the feedback component is further configured to receive the amplified outputs and to determine the actual analog gains based on the amplified outputs.
 11. The system of claim 1, wherein the feedback component is further configured to employ linear regression to determine the actual analog gains.
 12. The system of claim 1, wherein the feedback component is further configured to retain the plurality of calibration values in a data store for retrieval by the digital amplifier during video capture, wherein each calibration value of the plurality of calibration values is associated, in the data store, with the nominal analog gain setting used to determine the calibration value.
 13. The system of claim 1, further comprising an optimization component configured to utilize information determined by the feedback component to modify a resource associated with the sensor imager.
 14. The system of claim 1, further comprising a data store comprising a lookup table that maintains the plurality of calibration values in association with the plurality of nominal analog gain settings, wherein the feedback component is further configured to retrieve the at least one of the plurality of calibration values from the lookup table during operation of the sensor imager based on a value of the nominal analog gain setting.
 15. A method that facilitates compensating for variation associated with analog components of a sensor imager, comprising: applying analog amplification to test signals from a plurality of column buffers set to a nominal gain setting to yield a plurality of amplified analog outputs respectively associated with the plurality of column buffers; averaging actual gains of the plurality of amplified analog outputs to yield an average gain for the plurality of column buffers; comparing the nominal gain setting of the analog amplification to the average gain; determining, based on the comparing, a corrective digital amplification value corresponding to the nominal gain setting; and performing the applying, the averaging, the comparing, and the determining for a plurality of different nominal gain settings to determine respective corrective digital amplification values for the plurality of different nominal gain settings; and storing the corrective digital amplification values in association with the plurality of different nominal gain settings for calibration of a digital amplifier.
 16. The method of claim 15, further comprising determining the actual gains based on output voltages of the amplified analog outputs.
 17. The method of claim 15, further comprising: applying the analog amplification to a plurality of test signals at the nominal gain setting; digitizing amplified outputs from the analog amplification respectively corresponding to the plurality of test signals to yield digitized amplified outputs; and analyzing the digitized amplified outputs to determine at least one of the actual gains by employing a linear regression technique upon the digitized amplified outputs and the corresponding plurality of test signals.
 18. The method of claim 15, wherein the storing comprises storing the corrective digital amplification values in a lookup table in association with the respective plurality of different nominal gain settings the respective plurality of nominal gains.
 19. A system that enables calibrating gain associated with a sensor imager, comprising: means for amplifying a test signal according to a nominal analog gain setting of a plurality of column buffers to yield respective amplified analog signals for the plurality of column buffers; means for comparing an average analog gain measured for the amplified analog signals from the plurality of column buffers with the nominal analog gain setting to yield a calibration coefficient; and means for storing a plurality of calibration coefficients, including the calibration coefficient, respectively corresponding to a plurality of different nominal analog gain settings for utilization by a digital amplifier to correct a difference between the nominal analog gain setting and the average analog gain.
 20. The system of claim 19, further comprising means for storing the plurality of calibration coefficients in a lookup table that respectively associates the plurality of calibration coefficients with the plurality of different nominal analog gain settings. 